This invention relates generally to electron beams deflection systems for cathode ray tubes, and more particularly, to a magnetic deflection system having coil windings disposed in slots of a coil form.
German patent reference DE-OS No. 28 07 978 teaches that it is difficult to achieve a suitable shape for a magnetic field produced by the windings of a cathode ray tube (CRT) deflection yoke of the type which conforms to the flared shape of the CRT envelope. The reference further states that the higher sensitivity of saddle-shaped coils with respect to toroid coils renders the production of suitable field shapes particularly difficult. Accordingly, the designers of CRT equipment have heretofore encountered difficult design choices. On the one hand, it is desirable to extend the portion of the electron beam axis throughout which the electron beam of the CRT is under the influence of the magnetic deflection field so as to achieve improved deflection sensitivity. However, such a technique would require either a lengthening of the neck of the envelope, which is generally undesirable, or the mounting of the deflection coils partially around the flared portion of the envelope. It is a further problem, however, that the mounting of the deflection coils over the flared portion of the envelope increases the distance between the coils and the electron beam, thereby diminishing the degree of influence of the magnetic field over the electron beam.
The prior art has thrust at the problem of decreased sensitivity resulting from increased distance between the deflection coils and the electron beam by utilizing saddle-shaped coils. As indicated, although such coils have greater sensitivity than toroid coils, the production of a suitable magnetic field shape is difficult to achieve. In one prior art arrangement, saddle-shaped coils for one dimension of deflection are disposed in contact with the CRT envelope. The coils for the second dimension of deflection are disposed over the first set of coils, either as toroidal or as saddle-shaped coils. Accordingly, the second set of coils is disposed further from the electron beam than the first set of coils, thereby requiring much greater amounts of electric deflection power.
It is, therefore, an object of this invention to provide a deflection unit, which provides to the CRT a large modulation transfer function.
It is a further object of this invention to provide a deflection unit which is efficient in its use of electric deflection power and provides a relatively small amount of astigmatic distortion.
It is another object of this invention to provide a magnetic deflection system wherein the vertical and horizontal deflection coils have equal and minimum diameters around the electron beam axis.